1. Field of the Invention
The present invention relates to a method for preparing a gel containing nanometer titanium dioxide powders, and more particularly to a gel containing nanometer titanium dioxide powder in sizes ranging from 2 to 50 nm and having photocatalystic characteristic and self-cleaning efficiency in visible light.
2. Description of Related Art
Since 1970, most studies of titanium dioxide for manufacturing semiconductor have been subjected to photochemical reactions and semiconducting reactions on the present titanium dioxide particles. In these studies, crystalline configuration and grain sizes certainly affect the photochemical and semiconducting reactions. Preferably, anatase or anatase/rutile in the size of 30 nm is the optimal material. However, no study refers to the preparation and actual application to the titanium dioxide. Since 1990, titanium dioxide has been found to have great application in environmental cleaning and has actually been used since 1997. However, the studies still focus on the application but not the preparation of the titanium dioxide.
Conventional preparations of the titanium dioxide particles are divided into two types and are illustrated as follows:
1. Grinding pulverization: the titanium dioxide particles made by grinding are uneven in particle sizes as of 10 to 500 nm and have non-united crystalline configurations. Therefore, the titanium dioxide particles do not have photocatalytic characteristic and self-cleaning efficiency and are only applied in paints, cosmetics or correction fluids. Although the grinding method is improved by applying ultrasonic technology or adding acid solutions for chemical grinding to make the titanium dioxide particles even, the crystalline configuration of the titanium dioxide particles does not improve much.
2. Chemical synthesis: the chemical synthesis comprises three methods such as chemical vapor deposition (CVD) synthesis, organic solvent synthesis, and aqua synthesis. The chemical vapor deposition (CVD) method generates stable and highly pure titanium dioxide but is expensive in manufacturing. The organic solvent synthesis is to use titanium oxyalkyl (Ti(OR)4) to synthesize titanium dioxide particles, wherein the titanium oxyalkyl is sopped into an organic solvent such as glycol and heated to obtain titanium dioxide. However, the titanium oxyalkyl is expensive and operation must be carried out at a high temperature and a high pressure. Thus, the manufacturing cost of the organic solvent synthesis is not economic for manufacturers.
With regard to the aqua synthesis, titanium chloride (TiCl4) solution is mixed with a binding agent or an acid solution to heat to generate a gel containing titanium dioxide. However, chlorine ions are also generated which make the gel unstable and easily decomposed. Additionally, titanium dioxide made by the chemical synthesis is only efficient in ultraviolet light so that application of the gel containing titanium dioxide is limited.
According to the above description, the titanium dioxide is only used with ultraviolet light and that limits the application of the titanium dioxide. Therefore, the present invention has arisen to provide a method for preparing a gel containing nanometer titanium dioxide particles for visible light to improve the usage of the titanium dioxide.